This invention relates to the art of forming patterned films by the technology of vacuum film formation. More particularly, the invention relates to a method of forming patterned films by the technology of vacuum film formation at low cost and with high productivity.
Thin patterned films are formed on substrates by the technology of vacuum film formation (which are hereunder referred to as “vacuum thin films”) for use in a variety of applications including transparent and opaque electrodes for use in electronic displays such as liquid-crystal displays, light emitters (pixels) for use in electronic displays such as EL (electroluminescence), TFT (thin-film transistor) devices for use as switching devices in liquid-crystal displays, etc. and patterned magnetic media having a recording layer divided into 1-bit segments.
An exemplary method of forming patterned vacuum thin films on substrates comprises the steps of forming a continuous vacuum thin film on a surface of a substrate, then forming by photolithography a resist layer exposed in accordance with the pattern to be formed, and removing the unwanted thin film by dry or wet etching to pattern the vacuum thin film.
In another applicable method, a mask having openings that comply with the pattern to be formed is used and vacuum film formation is performed such that only the film forming material that passes through the mask is deposited on a substrate to form a patterned vacuum thin film.
In yet another applicable method, a continuous vacuum thin film is formed on a surface of a substrate and energy beams (e.g. laser beams) modulated in accordance with the pattern to be formed are applied either alone or in combination with the etching technology to form a patterned vacuum thin film.
A method for manufacturing a color Organic EL display disclosed in JP 2918087 B comprises the steps of subjecting a luminescent organic material to the evaporation onto a transfer substrate having highly thermal-conductive protrusions, which are patterned after the representing pixels, to thereby form a film, pressing the transfer substrate having the luminescent organic material formed thereon into the film against a transparent conductive film substrate (or a hole moving layer formed on a transparent conductive film), and sublimating the luminescent organic material by heating the protrusions of said transfer substrate so as to transfer the material to the surface of the transparent conductive film substrate.
However, these methods have their own problems with productivity, manufacturing cost, material options, etc.
The first-mentioned approach which utilizes photolithography provides high precision and definition in patterning; however, on account of the need for a large number of steps including the cleaning of the substrate, application of a resist, pre-bake, exposure and post-bake of the applied resist, development and etching, this approach requires massive initial investment and yet the yield of production is low. Because of the great number of steps involved and the low production yield, the first approach is costly and yet low in productivity.
In the second method which uses a mask to form a patterned vacuum thin film, the film forming material builds up on the mask as the film formation progresses. In the case of forming a precise and high-definition pattern, the mask having this buildup of the film forming material soon becomes unsuitable for use and must be changed or regenerated within a short time. This extra work lowers productivity and increases the manufacturing cost.
In order to form a precise pattern, vacuum film formation is preferably performed on the substrate as it is in contact with the mask. However, this increases the chance of damaging the substrate and the two members must be spaced apart. But then, the vapor of the film forming material and the like do not flow through the mask but get around it to blur the boundaries between individual elements of the pattern being formed.
In the method which uses energy beams modulated in accordance with the pattern to be formed, the need to scan the energy beams introduces difficulty in achieving high productivity. In order to improve productivity, a light source of high power is necessary but then the equipment cost increases and so does the complexity of the equipment mechanism. In addition, depending on the power of the energy to be applied, there is a limit on the film thickness that can be processed.
If energy beams are combined with the etching technology, an increased number of steps are involved and other disadvantages occur as are experienced in the first-mentioned photolithographic approach.
The problems existing in the above methods of forming patterned films can be solved by applying the method disclosed in JP 2918037 B to the formation of patterned films.
In the method of the Japanese patent, however, the transfer substrate is heated to a high temperature of near 500° C. so as to transfer the film forming material to a substrate (on which a film is to be formed) by the sublimation of the material, which makes it impossible to form a patterned film of a material with a lower heat resistance and confines the material for patterned film formation to those having a good sublimability or evaporability in view of the productivity. In addition, the transfer substrate having protrusions is required to be resistant to such temperatures as above. Accordingly, the patterned film forming material and the transfer substrate have only very narrow options so that the method of the Japanese patent is disadvantageous in terms of the choice or universality.